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Honeycomb Steers Light around Sharp Curves

Photonics.comMar 2015
ORLANDO, Fla., March 20, 2015 — Microscale plastic honeycomb structures can make light beams turn on a dime, a development that could allow more optical relays to be packed onto photonic integrated chips.

These spatially variant photonic crystals (SVPCs) were designed by researchers at the University of Texas at El Paso, then fabricated and tested at the University of Central Florida.

Using multiphoton direct laser writing, the Central Florida team created the structures out of the low-refractive-index photopolymer SU-8.

The red line depicts a light beam traveling and bending through the spatially variant photonic crystal lattice. The blue line shows how the light beam’s energy is conserved throughout the tight bend. Courtesy of the EM Lab/University of Texas at El Paso.
The researchers then directed 2.94-μm light beams through the lattices, which they found could direct the light around a 90° turn without loss. Additionally, the researchers found that the SVPCs bent vertically polarized light 25 times more effectively than horizontally polarized light.

Conventional waveguides like optical fibers can be used to steer light, but only through gradual bends. If the turn is too quick, the light beams escape and energy is lost.

Javier Pazos, who worked on the project while completing his doctorate at Texas, said the polymer used in the SVPC is ordinary and inexpensive, particularly when compared to other technologies attempting to manipulate light in the same way. Pazos now works for Intel, which is developing photonic integration technologies.

“The fact that we can do this with a simple plastic — an epoxy — is a pretty big deal,” Pazos said. “Normally, you need an exotic, unheard-of material to even attempt this.”

Other approaches to bending light beams have included graded photonic crystals and graded-index materials, both of which produce bending through refraction, the researchers wrote in Optics Express (doi: 10.1364/OE.22.025788 [open access]). SVPCs, on the other hand, bend light by diffraction.

Using light rather than electricity to carry information on computer chips could lead to big gains in speed and efficiency. “One of challenges when using light is figuring out a way to make tight bends so we can replace the metal wiring more effectively,” said Texas professor Dr. Raymond Rumpf.

Engineered optical elements like the SVPCs, and the technique used to create them, could hold the key.

“Direct laser writing has the potential to become a flexible means for manufacturing next-generation computer devices,” said Central Florida professor Dr. Stephen Kuebler.

With respect to light radiation, the restriction of the vibrations of the magnetic or electric field vector to a single plane. In a beam of electromagnetic radiation, the polarization direction is the direction of the electric field vector (with no distinction between positive and negative as the field oscillates back and forth). The polarization vector is always in the plane at right angles to the beam direction. Near some given stationary point in space the polarization direction in the beam...

As a wavefront of light passes by an opaque edge or through an opening, secondary weaker wavefronts are generated, apparently originating at that edge. These secondary wavefronts will interfere with the primary wavefront as well as with each other to form various diffraction patterns.